1. Field of the Invention
The present invention relates, to a method of preparing a patterned carbon nanotube array and a patterned carbon nanotube array prepared thereby. More particularly, the present invention relates to a method of preparing a patterned carbon nanotube array in which carbon nanotubes (“CNTs”) are uniformly arranged using porous templates, to a patterned CNT array prepared thereby and to a transparent electrode including the patterned CNT array and thus having high light transmittance.
2. Description of the Related Art
In accordance with the rapid development of information and communication technologies and the requirement for visualization of various information data, the demand for electronic displays continues to increase. Therefore, displays having a large size, a low price, high performance, high definition, slimness, and light weight are required. Particularly, corresponding to the ubiquitous computing era, in which information data can be obtained regardless of time and place, as a medium able to transfer the data anytime and anyplace, a flat panel display, which is easily portable, light, and slim, may be realized in a predetermined panel form, and further, may be folded like paper or rolled, is increasingly required to be developed.
Such a flat panel display includes a transparent electrode requiring fine patterning of a transparent conductive film. In order to realize the flexible display, an electrode material having high light transmittance and electrical conductivity and being flexible must be used.
The transparent electrode used in flat panel displays, such as plasma display panels (“PDPs”), field emission devices (“FEDs”), or vacuum fluorescent displays (“VFDs”), or in solar cells, is prepared by applying conductive metal oxide, such as indium oxide, indium tin oxide (“ITO”), tin oxide, aluminum tin oxide (“ATO”), or aluminum zinc oxide.
As such, the conductive metal oxide is applied through a sputtering process or a spray pyrolysis process, which is nevertheless disadvantageous because it is expensive and thus unsuitable for mass production. Further, in the flexible display, a conventional glass substrate should be replaced with a transparent flexible plastic substrate. In the case where the ITO transparent electrode is applied on the plastic substrate, it may be deformed due to the difference in coefficient of thermal expansion from the substrate, undesirably worsening adhesion or electrical conductivity.
With the goal of overcoming such problems, efforts have been made to provide transparent electrodes to replace the metal oxide film including ITO. For example, although techniques of suspending ITO particles in a polymer binder have been proposed, this ITO filled system cannot match the electrical conductivity of a continuous ITO film.
Furthermore, transparent conductive polymer materials are now being developed, such polymers typically requiring dopants to impart conductive properties. However, the presence of dopants is expected to have an adverse effect on control of the conductive properties, and may not be compatible with device miniaturization.
As the CNT network has been proven to have interesting electronic properties, such as electron mobility of 270 cm2/Vs (squared centimeters per Volt-second) and a transistor on-off ratio of about 104, techniques of binding originally flexible CNTs to a flexible polymer substrate to pattern them are receiving attention. The presently available patterned CNT array has been mainly prepared using a simple printing process or by preparing CNTs in a state of a photosensitive paste composition, which is then formed into a desired pattern through photolithography.
In this regard, Korean Patent Laid-open Publication No. 2005-35191 discloses a method of patterning a CNT coating by applying a CNT solution on a substrate to form a solid-state film, selectively impregnating the CNT film with a binder, and removing the portion of the film which is not impregnated with the binder.
In addition, Korean Patent Laid-open Publication No. 2005-108122 discloses a method of forming a finely patterned CNT array by patterning a photosensitive CNT paste through back exposure and removing the non-exposed portion using an organic solvent.
However, in the case where the pattern is formed using a photolithographic process, the patterning process is complicated and incurs a high cost. Further, in the case where the pattern is formed using a general printing process, the pattern has limited precision and thus is difficult to use to form a fine pattern.
As shown in FIG. 1, since CNTs 200 are not regularly formed but are randomly arranged, the uniformity of thickness and transmittance (as indicated by the arrows) are decreased. Consequently, when such CNTs 200 are applied to the transparent electrode 100 of a display or a photovoltaic device, problems occur in which the image quality of the display is deteriorated or the photovoltaic efficiency of the photovoltaic device is decreased.